Arsenic is widespread in Hillsborough County wells.
1 widespread, 5 rare out of 6 health checks.
From 127 wells tested in Hillsborough County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: radon (5).
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
1 in 3 people 134,778 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Hillsborough County compares with New Hampshire and the counties around it.
Each result puts Hillsborough County next to the 7 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Hillsborough County wells.
Arsenic22 of 127 wells over
Too few tested to show: Cheshire, Essex, MA, Merrimack, Sullivan.
These 5 are rare in Hillsborough County.
Manganese6 of 127 wells over
Too few tested to show: Cheshire, Essex, MA, Merrimack, Sullivan.
Uranium3 of 122 wells over
Too few tested to show: Cheshire, Essex, MA, Merrimack, Sullivan.
Fluoride0 of 13 wells over
Too few tested to show: Cheshire, Essex, MA, Merrimack, Sullivan.
Nitrate0 of 13 wells over
Too few tested to show: Cheshire, Essex, MA, Merrimack, Sullivan, Worcester, MA.
Lead0 of 51 wells over
Too few tested to show: Cheshire, Essex, MA, Merrimack, Sullivan.
Too few Hillsborough County wells were tested for this one.
Radon in water5 wells tested
None of the 1 Hillsborough County wells tested for bacteria had it, but every well needs a yearly test.
Coliform bacteria0 of 1 wells had it
E. coli0 of 1 wells had it
E. coli means human or animal waste is getting in, so if a test of your Hillsborough County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 18 of 127 tested wells, and it isn't a health risk.
Iron stains18 of 127 wells had it
Too few tested to show: Cheshire, Essex, MA, Merrimack, Sullivan.
Hillsborough County has 127 tested wells, and the busiest decade for testing was the 2010s.
None of the 127 wells has a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Hillsborough County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 3 things to check in Hillsborough County.
- Bacteria
- Nitrate
- Arsenic
What New Hampshire offers well owners
- Free testingWe didn't find a free program for all of New Hampshire. New Hampshire's private well page
- Certified labsNew Hampshire's list of certified labs
- Well recordsNew Hampshire's well record search
Here's what we know about radon and PFAS in Hillsborough County.
Hillsborough County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide
Between 2023 and 2025 the EPA had 9 town water systems in Hillsborough County test for PFAS. 4 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 9.0 ng/L of PFOA. Only 2 wells in Hillsborough County have public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Hillsborough County
Is well water in Hillsborough County safe to drink?
22 of 127 wells tested in Hillsborough County had arsenic over the limit, about 2 in 10. Across New Hampshire it's about 2 in 10. So test your own well for arsenic before you count on it.
Where can I get my well tested in Hillsborough County?
Use a lab New Hampshire has certified for drinking water. New Hampshire's list is linked above, in the box about testing. Ask for bacteria, nitrate and arsenic, the tests that matter most in Hillsborough County.
How does Hillsborough County compare with the counties around it?
For arsenic, the share of tested wells over the limit: 1 of the 3 neighboring counties with data had a higher share than Hillsborough County, at 17%. Rockingham had the most, at 29%. Groundwater doesn't stop at county lines, so Rockingham's 29% is worth knowing about if you live near it.
How often should I test my well in Hillsborough County?
None of the 1 wells tested for bacteria in Hillsborough County had it, but the CDC still says to test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Hillsborough County numbers come from
- People on wells: 134,778 in Hillsborough County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 634 well water samples from 127 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2019.
- Neighboring counties: the 7 counties that share a border with Hillsborough County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 9 town water systems in Hillsborough County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Hillsborough County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Department of Environmental Services, checked November 1, 2026.